1. Field of the Invention
The disclosure herein relates generally to the field of oil and gas production. More specifically, the present disclosure relates to a method and apparatus for initiating detonation of a perforating using wireless transmission.
2. Description of Related Art
Perforating systems are used for the purpose, among others, of making hydraulic communication passages, called perforations, in wellbores drilled through earth formations so that predetermined zones of the earth formations can be hydraulically connected to the wellbore. Perforations are needed because wellbores are typically completed by coaxially inserting a pipe or casing into the wellbore, and the casing is retained in the wellbore by pumping cement into the annular space between the wellbore and the casing. The cemented casing is provided in the wellbore for the specific purpose of hydraulically isolating from each other the various earth formations penetrated by the wellbore. As is known, hydrocarbon-bearing strata, such as reservoirs, exist within these formations. The wellbores typically intersect these reservoirs.
Perforating systems are used for perforating through the cement and casing into the surrounding subterranean formation. These systems typically comprise one or more perforating guns strung together, these strings of guns can sometimes surpass a thousand feet of perforating length. Included with the perforating guns are shaped charges that typically include a charge case, a liner, and a quantity of high explosive inserted between the liner and the charge case. When the high explosive is detonated, the force of the detonation collapses the liner and ejects it from one end of the charge at very high velocity in a pattern called a “jet”. The jet penetrates the casing, the cement and a quantity of the formation thereby forming a perforation in the formation that enables fluid communication between the wellbore and its surrounding formation.
FIG. 1 is a side partial cutaway view of a perforating system 5 comprising a perforating string 7 suspended within a wellbore 25. The perforating string 7 comprises a series of perforating guns 13 axially connected to one another by connecting subs 15. Tubing 9 is shown attached to the perforating string 7 and is a raising/lowering means for the perforating guns 13. The tubing 9 can also provide communication between the perforating string 7 and a surface truck 11. In some instances wireline is used in place of the tubing 9. The surface truck 11 typically includes a winch type device for disposal and retrieval of a perforating string 7 or instrument string in and out of the well. Also included within the surface truck 11 is an interface enabling surface personnel to transmit commands and receive data to and from the perforating string 7. The communicated data between the surface and the string 7 is generally provided along or by means of the tubing 9. The perforating string 7 of FIG. 1 is shown disposed in a deviated portion of the wellbore 25. For the purposes of illustration, perforations 21 are shown that extend from the wellbore 25, through the casing 17 that lines the wellbore 25, and into the surrounding formation 19.
The shaped charges are initiated by sending a signal from the surface to the perforating string 7 through the tubing 9. The signal is then received by a firing head 14 disposed on the upper portion of the perforating string 7. The firing head 14 transfers the firing signal to an initiator which then detonates an associated detonating cord. Typically the initiator is a type electrical blasting cap, an electrically-activated exploding bridge wire (“EBW”) initiator, an electrically activated exploding-foil initiator (“EFI”) or a percussively-activated explosive initiator. The explosive-filled tube is generally referred to as “detonating cord”. A type of detonating cord known in the art is sold by the Ensign-Bickford Company under the trade name PRIMACORD®. A resulting detonation wave passes along the length of the detonating cord that in turn initiates detonation of the connected shaped charges.
FIG. 2 shows an example of a section of a perforating gun 13 being detonated within a wellbore 25. As shown, the perforating gun 13 includes shaped charges 16 having a connected detonation cord 18. Some of the shaped charges 16 have been detonated thereby producing perforations 21 extending into the corresponding formation 19. A portion of the detonating cord 18 is missing proximate to the shaped charges having already been detonated demonstrating how the cord has been consumed by the detonating pressure wave. Thus, it is illustrated how the sequential detonation of adjacent shaped charges takes place in a particular perforating gun producing perforations extending through a casing 17 and to the corresponding formation 19.